I'll start with Andy's analogy, but come to a very different conclusion.
The Interstate Highway analogy isn't perfect, but I agree with Andy that it will do the job for this discussion. However, the impact of a non-neutral net isn't quite as Andy described (tolls being charged for everyone). Rather, it's more like what's happened out here in California where we now have some toll roads that operate in parallel with the Interstate Highway system. These toll roads charge a toll to people who decide to travel on them because of their lower congestion. Nobody HAS to travel on them, and everybody can get to where they want to go just as they used to before there was a toll road (actually, the existence of the toll road actually improves the situation for everyone else, to the extent that it removes traffic from the Interstate).
On the Internet, the "backbone providers" are roughly analogous to the Interstate Highway system. Today, everybody gets to put their packets on the backbone and everybody gets treated equally. Actually, that's not precisely true -- the backbone is already rife with special routing agreements. These are the equivalent of private connecting toll roads between Interstates, wherein one telecomm company pays another to route traffic via these special routes. So to this limited extent, the net is already not "net neutral" -- but this hasn't caused any brouhaha because nobody's asking an end-user customer to pay for this (at least, not to my knowledge).
What the backbone providers are proposing sounds to me much like these toll roads we have out here. They're proposing to provide an especially fast service for those sites who are willing to pay for it. Generally speaking, of course, that will be those sites that have a commercial interest in high performance. So what exactly is wrong with this? It's not as though non-paying sites are going to get any slower -- they're not. They can still take that same old Interstate Highway they used to take. The companies who choose to take the toll road get extra service in return for their payment. How do any of us lose on that deal?
There's only one sense in which I can see that Joe Six-Pack loses: it's if you believe that the backbone providers will increase the capacity of the backbone anyway, to make their biggest customers happy -- and then we all get to take a free ride on the big new highway they build. To me, this seems naive and silly -- without the incentive of extra revenue, the backbone providers have NO incentive to build extra capacity to make everything run smooth and fast. Instead, they have every profit incentive to build just barely enough capacity to allow them to charge for all the traffic, and not one bit more. They make the same revenue for a slow delivery as they do for a fast delivery.
What they're proposing sounds to me like a perfectly good business-like, captilist move: they see a market need, and they'd like to provide a service to serve it.
I think we should let them.